The invention relates to an injection nozzle for use in a device for moulding an object of a thermoplastic material in an injection mould, comprising a nozzle with at least one feed channel running through it which is connected at one end to a supply of the thermoplastic material, and which connects at the other or bottom end to a jet passage, and at this end has a closing element which is connected to control means for moving said element, so that it can be moved from a position in which the jet passage is in open communication with the feed channel to a position in which said communication is broken. Such a nozzle is known from U.S. Pat. No. 4,330,258.
In the injection moulding of a thermoplastic material the material is injected in a hot, liquid state and under pressure through an injection nozzle into the mould cavity inside an injection mould. In this case, at the jet passage of the nozzle where the material goes into the mould cavity, there has to be an abrupt transition in the temperature from the channel running through the nozzle to the temperature of the mould cavity, in order to ensure that when the finished object is being removed from the mould or unmoulded a clean break is obtained between said object and the material still present in the jet passage. Such an abrupt temperature transition cannot, however, be achieved, since a certain heat transfer will always take place between the nozzle and the mould, due to the fact that in injection moulding very high pressures are applied, as a result of which the mould has to be of a high-grade metal and/or ceramic material.